Pin maestro version

Summary:
The Maestro team just released a new version of maestro which dies in our CI

This change pins the version to something we know it's working, so we can decide when to move to the next version

## Changelog
[Internal] - Pin Maestro version

Reviewed By: cortinico

Differential Revision: D60380466

fbshipit-source-id: af842b7922736cc08300ac3bceef2d6110bcd913